1. Field of the Invention
The present invention relates to a method for forming an SrTiO3 film and a computer readable storage medium.
2. Description of the Related Art
In recent years, integrated circuits for semiconductor devices have been increasingly highly integrated, so DRAMs are required to have memory cells with a smaller surface area and a larger storage capacity. Due to such requirement, capacitors having an MIM (metal-insulator-metal) structure have attracted attention. In a capacitor having an MIM structure of this kind, a high dielectric constant material, such as strontium titanate (SrTiO3), is used as an insulating film (dielectric film).
Conventionally, where an SrTiO3 film for a DRAM capacitor is formed, Sr(DPM)2 is used as an Sr source material. However, Sr(DPM)2 has a low vapor pressure and a low adsorption rate on a substrate surface, and thus entails a problem in that the film formation rate is very low and thereby provides low throughput. In order to supply Sr(DPM)2 in a gaseous phase, this material needs to be heated to a temperature higher than 200° C., Accordingly, a heat-resistant material needs to be used for the piping lines, thereby increasing the apparatus cost.
As a technique to solve this problem, Jpn. Pat. Appln. KOKAI Publication No. 7-249616 (Patent Document 1) discloses a technique for forming an SrTiO3 film by use of Sr(C5(CH3)5)2 as an Sr source material. This document describes that an Sr compound containing Sr(C5(CH3)5)2 is dissolved in an organic solvent to form a liquid source material, which is then vaporized and supplied into a reaction chamber, so that the material is decomposed near a substrate surface to deposit an Sr-containing dielectric film on the substrate surface (claim 1 and so forth). Further, this document describes that an SrTiO3 film is formed by supplying an Sr compound and an organic metal complex substantially containing Ti (claim 9 and so forth).
In recent years, the aspect ratio of holes used for forming DRAM capacitors has been increased. In this respect, it has been found that, where an SrTiO3 film is formed by the method using the Sr source material and substrate disclosed in Patent Document 1 described above, the reaction is preferentially caused on the substrate surface and does not provide a good coverage inside holes having a high aspect ratio. Further, where an Sr source material and a Ti source material are supplied substantially at the same time, the reaction can be hardly uniformly caused to make a uniform composition over the top, side, and bottom surfaces of holes having a high aspect ratio.